WASHINGTON - The mighty U.S. arsenal of nuclear weapons, midwived by World War II and nurtured by the Cold War, is declining in power and purpose while the military's competence in handling the world's most dangerous arms has eroded. At the same time, international efforts to contain the spread of such weapons look ineffective.

Defense Secretary Robert Gates, for one, wants the next president to think about what nuclear middle-age and decline means for national security.

Gates joins a growing debate about the reliability and future credibility of the American arsenal with his first extensive speech on nuclear arms Tuesday. The debate is attracting increasing attention inside the Pentagon even as the military is preoccupied with fighting insurgencies in Iraq and Afghanistan. The unconventional tools of war there include covert commandos, but not nuclear weapons.

Gates is expected to call for increased commitment to preserving the deterrent value of atomic weapons. Their chief function has evolved from first stopping the Nazis and Japanese, then the Soviets. Now the vast U.S. stockpile serves mainly to make any other nation think twice about developing or using even a crude nuclear device of its own.

The chairman of the Joint Chiefs of Staff, Adm. Mike Mullen, wrote in the current issue of an internal publication, Joint Force Quarterly, that the United States is overdue to retool its nuclear strategy. He referred to nuclear deterrence - the idea that the credible threat of U.S. nuclear retaliation is enough by itself to stop a potential enemy from striking first with a weapon of mass destruction.

"Many, if not most, of the individuals who worked deterrence in the 1970s and 1980s - the real experts at this discipline - are not doing it anymore," Mullen wrote. "And we have not even tried to find their replacements."

Gen. Kevin Chilton, commander of U.S. Strategic Command, which is responsible for maintaining the nation's nuclear war plans, told Congress last spring that technical nuclear expertise also is lagging.